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BY 111 IS!)Ci Syscr stated that tlic lyiiipli glatids in sliecp aid cow enibryos arise froiii a plexus of lymphatic vessels.‘ “The connectirc- tissuc between the lymphatic! vessels of the plcsns has at first a trabecular arrangement, but later one or iiiore coin1)aet masses or islands are foriiied within it. From the Legiiiiiiiig, the conncctiw tissuc which iiiakes the trabccnlae, or niasws, is ~iarrowcriiieshed than that which surrouiids it, and contaiiis niaiiy blood vcsscls.” However, he adds: “There can be 110 doubt that there are inaiiy plexiis forinations in embryonic tissue, hariiig exactly the appearance uf those from which lymph glands arise, which simply degenerate.” Kliiig, in 1901, emphasizeil the iiuportance of the plexus stay aiid modelled the lyniphoid trabeculae.2 Although they connect with one another so as to form a continuous mass, his model has “an extremely irregular appcarancc.” It shows that these structured have little resemblance to the futnre glands. Kliiig stated that from such a general mass portions were separated by constriction to foriii the basis for individual gla~ids. Rut “Iyniph glaiids which have an isolated position appear froni the first as solitary foriliatioils ; each one arises independently.” A year later Miss Sabin wrote:” “All of the iiorlrs of the early ’Saser, F., 1’el:er die E:nt\\-ickeliiiig nnd den Bail cler iioriiialeii Lyu1p11- tlriisen. hint. EIeftc, 1WO. rol. C,, 1’1). .%O-532. Xliiig, C. A., Studien iitiar die Eiitwic.lching dpr Lyiiiplidriirzen beiin Menschen. Arch. f. inikr. Anat., 1904, vol. (3, ])[L B’iWilO. Y+abin, F. R., The developiiieiit of the lyinphatic nodes in the Iiig cult1 their relation to the lymph he‘nrts. .\mer. Joiirn. of Anat., 1905, vo1. 4, pp. ;%55-3m. (341) ttiibryos, the priiriary iiotlcs in the sense of Gulland, pass through this (plexus) stage. Lynipliatic nodes which clevelop later in the life of the t.ml)ryo, after lymphocytes occur, hurry through the primary process and show a considerable modification of it.” Recently4 I)r. Sabin published the figure of a section through the jugular lymph sac in a human embryo of 30 nim., “to show the simplc bridging of the sac which is the adage of the first lyinph node.” In thc pig she found that “the first node to appear develops from thc lymph heart, which is in the snpr a-cl av ic ular triangle be11 iiid the stcrnocleido- iriastoid muscle.” This, Saxcr, Kliiig and Miss Sabin agrw that thc first lymph glands arise from trabecnlac in a plexus of lyniphatic vessels. The plesiis of lymphatics in relatioii with thc iiitcrnal jugular veiii is a conspicuoiis featurc in human embryos iiicasuring from 30 to 40 iiiiri. Tt is showwi iii Figs. 1 ant1 2 from an embryo of 42 mm. A por- tion of the vein is sccii iii the lowcr right coriiw of each photograph. Iii places the coniiwtivc tissw trahecwlac arc broad aiiil pale, a< shown iii Fig. 1. Elsewhere they are morc slciider and deeply stain- iiig, as in the left part of Fig. 1 aiici in Fig. 2. Thc latter is a sec*tioii through the structure whicah Miss Sabin has closcribcd as the priinwy lpph gland. The cells in the similar trabeculae of a 31 mm. human embryo art! described by Kling as having “chiefly, if not exclusively, thc char- *Sabin, 1’. R., The lyinphritic systeiii iii Iruiiiaii eiilbryos, with a con- sideration of the 111oi~111ologyof the systeiii as a wholc. Aiuer. Joiirii. of .Illat., 1909, vol. 9, py. 43-91. ~ ~- __ __ ESL’LANATION OF FIGS. 1-6. FIGS.1 mid 2.--I’lesus of lymphatic rerscls in reliltion with tlie jiiternal jugular rein. From a hnina1i eiiibryo of 42 inin. x 46 dinins. (Harvartl Einbryologicnl Collection, Series 841, Section 432, aiid Series 838, Sectioii 153, respectively). Fras. 3, 4, niid 5.-Lyiiipli glands froiii a huiiian embryo of 42 111111. X 60 diains. E’ig. 3 shows tlir suhiiimtcll (“subinaxillary”) gland (Series 841, Section 569) ; Fig. 4 shows tlie external jugular glaiid (Serles S41, Section 534) ; nnd Fig. 5, the circunifl1.x scapular gland (Series 838, Scctioii 321). Fro. G.--Snbscalnilar Iymldi pliiiid froiii a rribbit of 20 days, 29 iilin. X 60 diiiiiis. (11. 14:. C., Series 170, Section l0SO.) 344 Frederic T. Ikwis. acter of fixed coniiective tissue cclls.” At 70 niin. “me fiiid amoiig palc oval nuclei, others of rounder form aid darker stain which ahead) suggest adenoid tissue.” Similarly, in pigs of 80 nim. Mibs Sabin found largc, faintly staining, oval nuclei belonging to conncc- tive tissue, and small, round, cleeply staining nuclei with coarser chromatin granules and a more distinct membrane, which belong ta lyrnphocytes. “Retwecn thc connective tissue cell, especially the young forms, and the lymphocyte oiic can see every possiblc transi- tion” (1905, p. 371). Saser likewisc~found that “the lymphocyttbs, which latw forin the biilk of the lymph glaiids, arisc in loco.” The esaniination of the bridges in the 42 111111. ciii1)rpo shows the palc oval cells arid the darker round ones appareiitly dcrivd froii them, and indicates that these trabeculae contain lymphoid tiusw. They do not, however, constitute a lymph gland, hut represent thc material from which the chain of deep cervical lymph glaiids is to be derived. A suficicntly detailed study of the later stages of the plesiis has not get been made. RonliOtJ believes that it prodiicos the “inter- scapular gland” of IEatai, which seeins to bc a collective term for the cervical fat and lymph glands. Almost simultaneously with the lymphoid transformation of tra- brcirlae among the jugular lymphatics, distinct lymph glands appear in the superficial tissues. These do not pass through a plexus stage, hut from the first they resemble the glands of the adult. The striking difference in the arrangement of the deep and the superficial lymphoid tissue seems due to the fact that the deep tissue is molded about an involved pre-existing plesus ; but thr superficial glands tlerclop freely in the loosc subcutanrow tissue. The plexus stagc niay thereforc be rcgarded as a complication in the development of the glands, rather than n fundamental condition which is sometimes hurried through, modified, or omitted. In t,he human embryo of 42 mm. two superficial glands were found on either side of the head. Their position is indicatcd in Fig. 7. The smaller gland is in intimate relation with the submental branch of the anterior facial vein. A section through it is shown in Fig. :{. &Bonnot, E.. The interscapular gland. Journ. of Anat. and Phys., 1908, vol. 43, pp. 4568. .\t thr iip1~~1)ordrr of the photograph a part of Illec*kcl'scwtilagc is .SWII oil the left, a11d the boiic of the lower jil\V oii the right ; the lower bort1t.r of the photograph passes throiigh the submaxillary glaiid. Betweeii the siibniasillarj gland aid the iiiaiitliblc the sulmieiital win appears, sn~~oinicledliy tlcnse tissue. This clciisc lyiiiphoid tissue is chiefly 011 the upper side of the veiii, aiitl it is bouiidcd by a lymphatic FIG. 7. FIG. 8. E'io. S.-'l'lie head of H huiiiaii eiiillryo of 42 iiiiii.. to show tlie positioii. of the suhiueiital ("subiiiiuilltir~")~iiitl esteriial jngnlar glniitls. x 3d/R iliains. (H. E. C., EM.) E'ic;. &--The liead of II ralibit eiiiliryo of 29 iiiiii. to show the position of the posterior facial glaiid. X 4 dianis. (11. E:. C., 170.) The veiiis sliowii are tlie anterior arid posterior facial, the liiiguo-facial, the external ~iidiiiteriinl jugular, iuid the j~igulo-c.e~ihalic.(The external jugular of iiiaii vorreslioiitls with tli6. jiipnlo-c.e]~litilic.of the ixbbit and iiot \villi (he li~iguo-facial; the latter iii tlie rall1)it is. howwer. ul;ually called tlie esleriial jugular. (:f. I,e\vis, Aiiier. Jonrii. of Ailat., vol. 9, 1,. 33.) vessel, c:rescentic iii seetioil. The snbiiieiittil wi!i sends braiiches into arid throiigh the lymph gland. The other lymph gland iii tlic licad is iii relatioil with the external jugular win. It is shown iu scction in Fig. P. Lymphoid tissues, enclosing small blood vcssels, fornis a roiuided iiiass attached to thc lower part of the vein. Its free surface is in relation with a crcb- ceritic lyinph sinus. No other 1pph glands were found in the head of this embryo. :Mi Frederic T. Lewis. In a human eiiibryo of 30 nim. the submental' aid external jiiguI;.iib glands were not found. They are not rrientioned in four embryos of 46-50 mm. described by Miss Sabin, but she has recorded that in an FIG.9.--Itecoiistruction of tlie artcries in the axilla of the hiininn eliibryo of 42 min., to show the positioii of the first axillary lymph gland. x 10 diaim (H. P:. C., 535). The suhscapular br:uicli of the asillary artery is seen to divide into the circumfles scapular and thorwco-dorsal arteries. The lyinph gland is aloiig the latter. The brachial and latcriil thoracic arteries are also shown. 80 Imn. einbryo "therc arc scw~iidarylynipli nodcs aloiig the veins of the neck; for esaiiiple, aloug the external jugular rein next thtt parotid gland and along the facial vein at the angle of the jaw." #It seems desirable to name the early lyniph glaiids for the veins which they accompany and this has been done. It is to be noted, however, that in the adult there are several glands along the submental vessels, the anterior ones forming the submental gronp. mid the posterior ones the submaxillary group. The submental gland of tlic 42 min. embryo belongs evidently with the submaxillary group of the adult.

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